Vernier machine with shaped permanent magnet groups

Abstract

An electric machine includes a rotor, permanent magnets, a stator, and a stator winding wound about a plurality of teeth to form a number of stator magnetic poles. The rotor includes a rotor core and a plurality of walls that form openings in the rotor core. A permanent magnet is mounted in each of the openings formed in the rotor core. The plurality of permanent magnets are arranged to form a plurality of groups of permanent magnets that are equally circumferentially distributed around the rotor core with an interior polarity on a side of each permanent magnet facing other permanent magnets of the group of permanent magnets to which the permanent magnet is associated that is the same for all of the permanent magnets. Each permanent magnet is arranged to form a rotor pole, wherein a number of rotor poles is greater than the number of stator magnetic poles.

What is claimed is: 
     
       1. An electric machine comprising:
 a stator comprising
 a stator core; and 
 a plurality of teeth that extend outward from the stator core, wherein a slot of a plurality of slots is positioned between a pair of the plurality of teeth; 
 
 a stator winding wound about the plurality of teeth to form a number of stator magnetic poles between a set of connectors, wherein the number of stator magnetic poles is equal to a number of the plurality of teeth divided by a number of phases, wherein the number of phases is defined for a current provided to the stator winding when the electric machine is operated; 
 a rotor comprising
 a rotor core; and 
 a plurality of walls that form openings in the rotor core that are separated from each other by the rotor core; and 
 
 a plurality of permanent magnets, wherein a permanent magnet is mounted in each of the openings formed in the rotor core, wherein the plurality of permanent magnets are arranged to form a plurality of pairs of permanent magnets that are equally circumferentially distributed around the rotor core, wherein each permanent magnet has an interior polarity and an exterior polarity, wherein the interior polarity has an opposite polarity relative to the exterior polarity, wherein the interior polarity is on a side of each permanent magnet facing other permanent magnets of the group of permanent magnets to which the permanent magnet is associated, wherein the interior polarity is the same for all of the permanent magnets; 
 wherein the stator is mounted on a first side of the rotor separated by an air gap between a surface of the rotor core and a tooth of the plurality of teeth; 
 wherein the openings further include a first flux barrier formed by a first plurality of walls of each opening on a first side of each permanent magnet that is closest to the stator, a second flux barrier formed by a second plurality of walls of each opening on the first side of each permanent magnet physically separated from the first flux barrier by the rotor core, and a third flux barrier formed by a third plurality of walls of each opening on a second side of each permanent magnet, wherein the first side is opposite the second side; 
 wherein each permanent magnet is arranged to form a rotor pole, 
 wherein a number of rotor poles is greater than the number of stator magnetic poles. 
 
     
     
       2. The electric machine of  claim 1 , wherein each pair of permanent magnets of the plurality of pairs of permanent magnets are arranged to form a V-shape open towards the plurality of teeth of the stator. 
     
     
       3. The electric machine of  claim 1 , wherein the third plurality of walls of each opening form three sides of a parallelogram, wherein a fourth side of the parallelogram is formed by a first face of a respective permanent magnet, wherein a first wall of the third plurality of walls is parallel to a second face of the respective permanent magnet, wherein a second wall of the third plurality of walls is parallel to a third face of the respective permanent magnet, wherein the first side is opposite the second side, wherein a third wall of the third plurality of walls connects between the first wall and the second wall and is parallel to the first face of the respective permanent magnet. 
     
     
       4. The electric machine of  claim 1 , wherein the first plurality of walls of each opening form two sides of a first triangle, wherein a third side of the first triangle is formed by a first portion of a first face of a respective permanent magnet, wherein the second plurality of walls of each opening form two sides of a second triangle, wherein a third side of the second triangle is formed by a second portion of the first face of the respective permanent magnet. 
     
     
       5. The electric machine of  claim 1 , wherein the number of rotor poles is selected as N p =2N S ±N SMP , where N p  is the number of rotor poles, N S  is the number of the plurality of teeth of the stator, and N SMP  is the number of stator magnetic poles. 
     
     
       6. The electric machine of  claim 5 , wherein the number of rotor poles is twenty, the number of the plurality of teeth of the stator is twelve, and the number of stator magnetic poles is four. 
     
     
       7. The electric machine of  claim 1 , wherein a rotor pole pitch angle is defined between a first axis and a second axis, wherein the first axis extends radially outward from a radial center of the rotor core through a center of a first wall of a first permanent magnet of each pair of permanent magnets, wherein the first wall is a closest wall of the first permanent magnet to an exterior surface of the rotor core, wherein the second axis extends radially outward from the radial center of the rotor core through a center of a second wall of a second permanent magnet of each pair of permanent magnets, wherein the second wall is a closest wall of the second permanent magnet to the exterior surface of the rotor core, wherein the rotor pole pitch angle is between 25% and 75% of a rotor pole pair pitch angle τ rpp , where τ rpp =360/N pG , where N pG  is a number of the plurality of pairs of permanent magnets. 
     
     
       8. The electric machine of  claim 1 , wherein each pair of permanent magnets includes a first permanent magnet and a second permanent magnet, wherein the first permanent magnet is mounted in its opening to form a mirror image of the second permanent magnet relative to a first axis that extends radially outward from a radial center of the rotor core through a center of the pair of permanent magnets to which the first permanent magnet and the second permanent magnet are associated. 
     
     
       9. The electric machine of  claim 3 , wherein a minimum distance is defined between the third flux barrier of a first permanent magnet of each pair of permanent magnets and the third flux barrier of a second permanent magnet of each pair of permanent magnets, wherein the minimum distance is between 0.1% and 25% of a width of each permanent magnet. 
     
     
       10. The electric machine of  claim 9 , wherein a length of the first wall of the third flux barrier associated with each permanent magnet of the plurality of permanent magnets is between 0.1% and 50% of a length of the second face of each permanent magnet. 
     
     
       11. The electric machine of  claim 1 , wherein an outer radius of the rotor core is between 10% and 95% of an outer radius of the stator core. 
     
     
       12. The electric machine of  claim 1 , wherein a radial length of the rotor core is between 5% and 95% of an outer radius of the stator core. 
     
     
       13. The electric machine of  claim 12 , wherein a length of each permanent magnet is between 0.1% and 100% of the radial length of the rotor core. 
     
     
       14. The electric machine of  claim 1 , wherein a width of each permanent magnet is between 0.1 and 50 times a length of the air gap. 
     
     
       15. An electric machine comprising:
 a stator comprising
 a stator core; and 
 a plurality of teeth that extend outward from the stator core, wherein a slot of a plurality of slots is positioned between a pair of the plurality of teeth; 
 
 a stator winding wound about the plurality of teeth to form a number of stator magnetic poles between a set of connectors, wherein the number of stator magnetic poles is equal to a number of the plurality of teeth divided by a number of phases, wherein the number of phases is defined for a current provided to the stator winding when the electric machine is operated; 
 a rotor comprising
 a rotor core; and 
 a plurality of walls that form a first plurality of openings and a second plurality of openings in the rotor core that are separated from each other by the rotor core; and 
 
 a plurality of permanent magnets, wherein a permanent magnet is mounted in each of the openings formed in the rotor core, wherein the plurality of permanent magnets are arranged to form a plurality of groups of permanent magnets that are equally circumferentially distributed around the rotor core, wherein each permanent magnet has an interior polarity and an exterior polarity, wherein the interior polarity has an opposite polarity relative to the exterior polarity, wherein the interior polarity is on a side of each permanent magnet facing other permanent magnets of the group of permanent magnets to which the permanent magnet is associated, wherein the interior polarity is the same for all of the permanent magnets, wherein each group of permanent magnets of the plurality of groups of permanent magnets includes a first permanent magnet, a second permanent magnet, and a third permanent magnet, wherein the third permanent magnet is between a respective first permanent magnet and a respective second permanent magnet to form a U-shape open towards the plurality of teeth of the stator; 
 wherein the stator is mounted on a first side of the rotor separated by an air gap between a surface of the rotor core and a tooth of the plurality of teeth; 
 wherein the first plurality of openings include a first flux barrier formed by a first plurality of walls of each respective opening of the first plurality of openings on a first side of each first permanent magnet and of each second permanent magnet that are closest to the stator, a second flux barrier formed by a second plurality of walls of each respective opening of the first plurality of openings on the first side of each first permanent magnet and on the first side of each second permanent magnet, and a third flux barrier formed by a third plurality of walls of each respective opening of the first plurality of openings on a second side of each first permanent magnet and of each second permanent magnet, wherein the first side is opposite the second side, wherein the first flux barrier of each first permanent magnet and of each second permanent magnet is physically separated from the respective second flux barrier by the rotor core, 
 wherein the second plurality of openings include a fourth flux barrier formed by a fourth plurality of walls of each respective opening of the second plurality of openings on a first side of each third permanent magnet and a fifth flux barrier formed by a fifth plurality of walls of each respective opening of the second plurality of openings on a second side of each third permanent magnet, wherein the first side of each third permanent magnet is opposite the second side of each third permanent magnet; 
 wherein each permanent magnet is arranged to form a rotor pole, 
 wherein a number of rotor poles is greater than twice the number of stator magnetic poles. 
 
     
     
       16. The electric machine of  claim 15 , wherein a minimum distance is defined between the third flux barrier of the first permanent magnet of each group of permanent magnets and the fourth flux barrier of the third permanent magnet of each group of permanent magnets, wherein the minimum distance is between 0.1% and 25% of a width of each permanent magnet. 
     
     
       17. The electric machine of  claim 16 , wherein the minimum distance is further defined between the third flux barrier of the second permanent magnet of each group of permanent magnets and the fifth flux barrier of the third permanent magnet of each group of permanent magnets. 
     
     
       18. The electric machine of  claim 15 , wherein the first plurality of walls and the second plurality of walls form two sides of a triangle, wherein a third side of the triangle is formed by a portion of a first face of a respective permanent magnet. 
     
     
       19. The electric machine of  claim 15 , wherein the number of rotor poles is selected as N p =2N S ±N SMP , where N p  is the number of rotor poles, N S  is the number of the plurality of teeth of the stator, and N SMP  is the number of stator magnetic poles. 
     
     
       20. The electric machine of  claim 15 , wherein the first permanent magnet of each group is mounted in its opening to form a mirror image of the second permanent magnet relative to a first axis that extends radially outward from a radial center of the rotor core through a center of the group of permanent magnets to which the first permanent magnet and the second permanent magnet are associated.